In an EPS (evolved packet system) of an LTE (long term evolution) system, an SGW (serving gateway) has a corresponding serving area, and the granularity of the serving area is a TA (tracking area). The serving areas of different SGWs may be overlapped. An MME (mobility management entity) selects an SGW for a UE (user equipment) based on a network topology structure.
When a UE triggers a TAU (tracking area update) in which a TA is changed in a moving process, if a TA that the UE newly enters is not located in the serving area of an original SGW accessed by the UE, the MME may select a new SGW for the UE. If an evolved base station (eNodeB) accessed by the UE is not changed at this moment, since the SGW is changed, an IP (Internet protocol) address and a TEID (tunnel endpoint identifier) of the UE bearer at the SGW side on an S1-U interface (an interface in a 3GPP protocol) will change. However, at this moment, the eNodeB cannot learn the change of the bearer uplink IP address and TEID of the UE, thus resulting in a service interruption of the UE, and the UE service cannot be recovered before the UE accesses a network again or performs switching of the SGW.
The scenario above is described below in detail from two aspects.
Firstly, a scenario condition of a scenario where “since a tracking area update (TAU) in which an evolved base station (eNodeB) is not changed and a serving gateway (SGW) is changed occurs to a user equipment (UE), a service interruption of the UE is resulted in after the TAU process is completed” is specified as follows.
An MME maintains a plurality of tracking area lists (TA lists), wherein TACs (tracking area codes) contained in two TA lists therein are as follows:                TA List1={TAC0, TAC1, TAC2, TAC3 . . . }; and        TA List2={TAC4, TAC5, TAC6 . . . }.        
TAC values contained in these two TA lists do not have any intersection, and respectively correspond to serving areas of two SGWs. TA List1 corresponds to SGW1, and TA List2 corresponds to SGW2. The MME, SGW1 and SGW2 are all coupled to the eNodeB which serves for cell A and cell B, the TAC of cell A is TAC 1, and the TAC of cell B is TAC 4.
On the basis of the scenario condition above, the scenario above is further divided into two different scenarios according to two reasons triggering the TAU, and the two scenarios are discussed respectively in combination with FIG. 1 and FIG. 2 as follows.
Scenario I, the UE does not move, and a cell TAC configuration modification at the eNodeB side triggers the UE to initiate a TAU where the TA is changed.
Referring to FIG. 1, in this scenario, the eNodeB supports the TACs in TA List1 and TA List 2 simultaneously. The UE is accessed in cell A under the eNodeB, the TAC of cell A is TAC=TAC 1, and SGW1 is accessed at a core network side. At this moment, the TAC of cell A is manually modified at the eNodeB side from TAC 1 to TAC 4, thereby triggering the eNodeB to issue update broadcast information. After receiving the broadcast, the UE finds that the TA is changed, thereby triggering a TAU flow changing the TA. The MME finds that the TAC of the TA where the UE is located when initiating the TAU is TAC 4, belonging to TA List2, and corresponding to the serving area of SGW2. At this moment, the MME reselects an SGW for the UE, creates bearer context (including the bearer uplink IP address and TED of the UE) for the UE on SGW2, and deletes bearer context (including the bearer uplink IP address and TEID of the UE) of the UE in SGW1. After the TAU is successful, the MME replies with a tracking area update accept message to the UE. However, in this TAU process, there is no signalling message on an S1 interface to notify the eNodeB that the SGW accessed by the UE has been changed, and thus the eNodeB will still forward an uplink service packet of the UE to SGW1. However, at this moment, the bearer context (including the bearer uplink IP address and TEID of the UE) of the UE has been deleted in SGW1, and although SGW1 has received the uplink service packet of the UE, SGW1 cannot perform an operation of the next step, resulting in a service interruption of the UE.
Scenario II, the UE moves in the eNodeB, and a cell change at the eNodeB side triggers the UE to initiate a TAU in which the TA is changed.
Referring to FIG. 2, in this scenario, the eNodeB supports the TACs in TA List1 and TA List 2 simultaneously. The UE is accessed in cell A under the eNodeB, the TAC of cell A is TAC=TAC 1, SGW1 is accessed at a core network side, and the TAC of cell B of the eNodeB is TAC=TAC 4. The UE switches from cell A to cell B, and after the switching is completed, the UE finds that the TA is changed and therefore initiates a TAU. The MME finds that the TAC of the TAU initiated by the UE is TAC 4, belonging to TA List2, and corresponding to the serving area of SGW2. At this moment, the MME reselects an SGW for the UE, creates bearer context (including the bearer uplink IP address and TEID of the UE) for the UE on SGW2, and deletes bearer context (including the bearer uplink IP address and TEID of the UE) of the UE in SGW1. After the TAU is successful, the MME replies with a tracking area update accept message to the UE. However, in this TAU process, there is no signalling on an S1 interface to notify the eNodeB that the SGW accessed by the UE has been changed, and thus the eNodeB will still forward an uplink service packet of the UE to SGW1. However, at this moment, the bearer context (including the bearer uplink IP address and TEID of the UE) of the UE has been deleted in SGW1, and although SGW1 has received the uplink service packet of the UE, SGW1 cannot perform an operation of the next step, resulting in a service interruption of the UE.
With regard to the problem in the related art of resulting in a UE service interruption since an evolved base station (eNodeB) cannot learn that the bearer uplink IP address and TEID of the UE are changed in the scenarios above, there is no effective solution proposed yet.